PAPER making! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ® FROM THE PUBLISHERS OF PAPER TE Volume 8, Number 2, 2022
Lignin Inter-Diffusion Underlying Improved Mechanical Performance of Hot-Pressed Paper Webs AMANDA MATTSSON 1 , TOVE JOELSSON 1,2 , ARTTU MIETTINEN 3,4 , JUKKA A. KETOJA 1,4 , GUNILLA PETTERSSON 1 & PER ENGSTRAND 1 . Broader use of bio-based fibres in packaging becomes possible when the mechanical properties of fibre materials exceed those of conventional paperboard. Hot-pressing provides an efficient method to improve both the wet and dry strength of lignin-containing paper webs. Here we study varied pressing conditions for webs formed with thermomechanical pulp (TMP). The results are compared against similar data for a wide range of other fibre types. In addition to standard strength and structural measurements, we characterise the induced structural changes with X-ray microtomography and scanning electron microscopy. The wet strength generally increases monotonously up to a very high pressing temperature of 270°C. The stronger bonding of wet fibres can be explained by the inter-diffusion of lignin macromolecules with an activation energy around 26 kJ mol -1 after lignin softening. The associated exponential acceleration of diffusion with temperature dominates over other factors such as process dynamics or final material density in setting wet strength. The optimum pressing temperature for dry strength is generally lower, around 200°C, beyond which hemicellulose degradation begins. By varying the solids content prior to hot-pressing for the TMP sheets, the highest wet strength is achieved for the completely dry web, while no strong correlation was observed for the dry strength. Contact information: 1. Department of Chemical Engineering, Mid Sweden University, SE-85170 Sundsvall, Sweden. 2. MoRe Research Örnsköldsvik AB, Box 70, SE-89122 Örnsköldsvik, Sweden. 3. Department of Physics, University of Jyvaskyla, P.O. Box 35, FI-40014 Jyvaskyla, Finland. 4. VTT Technical Research Centre of Finland Ltd., P.O. Box 1000, FI-02044 Espoo, Finland.
Polymers 2021, 13, 2485. https://doi.org/10.3390/polym13152485 Creative Commons Attribution International License 4.0
The Paper Industry Technical Association (PITA) is an independent organisation which operates for the general benefit of its members – both individual and corporate – dedicated to promoting and improving the technical and scientific knowledge of those working in the UK pulp and paper industry. Formed in 1960, it serves the Industry, both manufacturers and suppliers, by providing a forum for members to meet and network; it organises visits, conferences and training seminars that cover all aspects of papermaking science. It also publishes the prestigious journal Paper Technology International ® and the PITA Annual Review , both sent free to members, and a range of other technical publications which include conference proceedings and the acclaimed Essential Guide to Aqueous Coating .
Article 2 – Hot Pressing
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